Add Trapping Rain Water algorithm in Java

[SURYANSHUAGRAWAL2006]

Description

Implemented Trapping Rain Water algorithm in Java.

• Used O(n) time and O(1) space approach.
• Solved using for-loops and if-else statements without extra arrays.
• File and class follow PascalCase: TrappingRainWater.java / TrappingRainWater.
• Package: com.thealgorithms.dynamicprogramming
• No Scanner or System.out.print statements, fully compatible with automated tests.
• Problem reference: https://leetcode.com/problems/trapping-rain-water/

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.96%. Comparing base (48ba1ae) to head (0085e6c).

Files with missing lines	Patch %	Lines
...gorithms/dynamicprogramming/TrappingRainWater.java	0.00%	29 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6920      +/-   ##
============================================
- Coverage     78.05%   77.96%   -0.10%     
- Complexity     6466     6467       +1     
============================================
  Files           738      739       +1     
  Lines         21585    21614      +29     
  Branches       4220     4231      +11     
============================================
+ Hits          16849    16851       +2     
- Misses         4064     4092      +28     
+ Partials        672      671       -1     

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[SURYANSHUAGRAWAL2006]

"if there's any change or format issue, please let me know. I'll fix it quickly".